did you try to ‘save as’ a new project?
in this post , error 4 , seemed to be related to saving over an existing project … though we didn’t get much more in the way of details.
if you contact Squarp (as above) , then hopefully they can tell you id this is more an ‘application error’ or an issue with writing to the sdcard (so physical) .
similarly they can tell you what ‘error 8’ is - though, Id hazard a guess that is simply going to be a ‘corrupt’ project error.
frustrating, indeed, if you search the forum - you’ll see its only be mentioned once (that I could find), so not a common issue - so unfortunatly, id guess its likely a sdcard issue… they, are pretty reliable usually, but they do fail … could just be an ‘unlucky’ bad one 
(sdcard type all be pretty much irrelevant … its not used ‘real time’, so pretty much anything will work in it… just might be slower for loading/saving projects)